Photographic products and processes using an image receiving web



United States Patent US. Cl. 96-29 9 Claims ABSTRACT OF THE DISCLOSURE Processes comprising vacuum deposition of precipitation nuclei on the surface of substrate permeable to monobath developer to render the substrate capable of forming a reverse visible image by contact with an exposed silver halide emulsion, such substrates capable of forming reverse visible images, and processes for forming reverse visible images on such substrates.

This invention relates to novel photographic materials and processes, and more specifically, it relates to diffusion transfer materials, the processes for producing such materials, and novel processes for developing photographic materials.

Diffusion transfer materials and processes are known in the photographic arts, one of the chief uses for such materials being in the copying of papers, documents, books, and the like. In such copying processes, a photosensitive silver halide-containing emulsion is exposed to light by some appropriate means, usually by the reflex copying of a printed surface, so as to form a latent negative image of the subject. This exposed emulsion is then contacted in the presence of certain chemicals, with the face of a nonphotosensitive emulsion which contains specks of silver or the like to serve as precipitation nuclei. The result of the process is a sheet containing a direct negative image and a sheet containing a reverse, or positive, image of the subject. The negative is discarded and the positive is retained as a photocopy of the original subject.

A similar process has been used to obtain a direct print from regular photographic negative materials where it is desired to have a usable positive as soon as possible. This system has found particular application in processing photosensitive negative materials which are used in the form of rolls, such as 16-mm., 35-mm., 70-mm., 5-inch and 9-inch films for cinematographic and aerial survey work. In this system, the surface of a specially prepared nonphotosensitive strip is contacted with the surface of the exposed photosensitive emulsion in the presence of certain chemicals so that the film is developed to form a negative, while a positive image for immediate viewing is simultaneously formed on the nonphotosensitive strip.

The nonphotosensitive strip is a gelatin-based emulsion coated on a flexible suport, the emulsion containing micro scopic bits of the precipitation nuclei. These minute particles of material are called precipitation nuclei or nucleating centers, because the silver complex which diffuses from the exposed photosensitive emulsion into the second strip emulsion is reduced to metallic silver in their presence. Thus, these minute particles act as nuclei for the formation of metallic silver.

These diffusion transfer processes are carried out using so-called monobath developers, that is, processing agents which contain both a developing agent and a silver halide solvent, or fixer. In areas where there is little or no exposure of the negative material, very little silver halide is reduced to metallic silver by the developer, and the solvent "ice forms complexes with the silver halide in the negative emulsion. The silver complex migrates, or diffuses, across the surface into the second emulsion with which the photo sensitive emulsion is in contact. The complexes are reduced to metallic silver in the presence of the precipitation nuclei. Thus, in an area of the negative where the negative emulsion has not been struck by light and is therefore clear, the nucleating centers will cause a heavy silver deposit to form on the second strip. Where the photosensitive emulsion is heavily exposed, practically all of the silver halide will be reduced to silver before it can be dissolved by the solubilizing agent, so that the second strip contains little silver in the areas where the negative is dark or contains much reduced silver. Thus, this diffusion transfer process produces a positive copy during development of the negative image.

The known diffusion transfer positive materials generally have a low resolving power. An increase in resolving power would produce a more useful positive material. Moreover, these materials involve the use of an ordinary gelatin emulsion which does not in all cases pass enough processing agent to develop the photosensitive emulsion when used as a processing mat. It would be desirable to prepare a second strip which could form a positive, or reverse, image by the diffusion transfer process and at the same time would readily pass sufficient monobath developer completely to develop the negative material. Such a process material would make possible the rapid processing of photographic negative materials and simultaneously produce a positive image. Thus, a relatively highresolution positive print for immediate study would be obtained and further positive prints could be obtained from the negative material.

This invention provides a novel diffusion transfer material having a higher resolution for the reverse images than has heretofore been obtained. Moreover, in another aspect this invention provides a monobath developersaturable processing web which is used simultaneously to develop an exposed silver halide emulsion and to form a reverse visible image on the surface of the processing web.

Certain other aspects of this invention provide methods of preparing high-resolution reverse image materials, and novel developing methods are also provided.

Further and more specific objects, features, and advantages will clearly appear from the detailed description given below.

Briefly, the product of this invention is a substrate which is permeable to monobath developers and which has precipitation nuclei deposited on its surface, the remainder of the substrate being essentially free of such nuclei. This substrate will form a reverse visible image when it is contacted with a silver halide emulsion which is being developed by a monobath-type developer.

A process of this invention comprises vacuum deposition of precipitation nuclei on the surface of substrates which are permeable to monobath developers. These substrates can either be hydrophilic, such as the gelatin normally used as a basis for photographic emulsions, or in the nature of a web material. In either event, the process renders the substrate capable of forming a reverse visible image by surface contact during the development of an exposed silver halide-containing emulsion.

The process of this invention for preparing finished fixed images comprises the steps of contacting an exposed silver halide emulsion with the surface of a substrate and with monobath developer, producing a reverse visible image on the substrate, and developing the silver halide emulsion, the substrate being coated with precipitation nuclei and being permeable to monobath developer.

The product of this invention has a higher resolving power than previously attainable with diffusion transfer materials of the kind described. Moreover, when the substrate is a web material, a more economical process can be provided since the web contains a reverse visible image for immediate inspection, Whereas in the past such webs have had little or no utility after development of the silver halide emulsion. Thus, this invention not only pro- 'vides novel materials, but also makes it possible to utilize substrates which heretofore were unavailable for dilfusion transfer processing.

As used herein, silver halide emulsions and silver halide-containing emulsions will be understood to mean conventional photo-sensitive emulsions containing silver halides, and particularly silver bromide, chloride, and iodide and mixtures thereof. Such emulsions generally consist chiefly of a dispersion of silver halide particles in gelatin. The emulsions are coated onto a support which is transparent if the emulsion is to be used for projection, for example as a slide or negative, and which is opaque if the emulsion is to be viewed by reflected light, such as in a print. In use, such silver halide emulsions are exposed to either particulate or electromagnetic energy, such as visible light, gamma radiation, beta radiation, and the like, so that when the emulsion is treated with a developing agent, the exposed areas become dark. The developable portions of the emulsion are said to form a latent image, and a silver halide emulsion containing a latent image will be referred to herein as an exposed silver halide emulsion.

For purposes of this disclosure, the surface upon which the precipitation nuclei are carried will be referred to as the substrate. It will be understood that this substrate must be permeable to mobile aqueous liquids, that is, it must freely permit the passage of aqueous liquids at least into its surface and can, if desired, be permeable to aqueous liquids throughout its depth. An example of a permeable substrate is a coating of hydrophilic material such as gelatin, polyvinyl alcohol, gum ara-bic, polyethylene-oxides or the like on an acetate film base or on paper. In the case of the acetate film base coated with gelatin, the gelatin is capable of having aqueous liquids diffuse into its surface, and hence is permeable to aqueous liquids. It will be understood that the hydrophilic layer can be carried on a wide variety of backing materials such as cellulose nitrate, glass, polyester, paper, and the like. For continuous high-speed processing of photographic negatives, flexible base is preferred.

In another aspect of this invention, the permeable substrate is a porous web of suitable material. For example the web can be a microporous, nonfibrous wettable mat of polyvinyl chloride. By wettable is meant having the ability to absorb and retain aqueous liquids. The permeable substrate can be a porous web or woven mat, exemplified by cellulose acetate, cellulose triacetate, polyurethane, fiberglass, paper, and the like. A microporous substrate is one in which the void space is comprised of a plurality of interconnected interstitial pore openings.

The surface of the novel substrates of this invention is coated with precipitation nuclei. Such precipitation nuclei are known in the art and are materials which cause the reduction of silver halide soluble complexes in the presence of suitable chemical agents. 'It is desirable in the practice of this invention that the precipitation nuclei be heavy metals or heavy-metal compounds. It is desirable to use metals of Groups I-B, II-B, IV-A, VI-A, and VIII or the reaction products of Group I-B, IIB, and IVA metals with sulfur or elements of Group VI-A. Preferred nucleating center compositions are copepr, tin, lead, mercury, germanium, palladium, and platinum and the sulfides, tellurides, and selenides thereof. Particularly pre ferred nucleating center compositions are gold, silver, gold sulfide, and silver sulfide. While it is possible to use combinations of two or more types of precipitation nuclei, it is preferred in the practice of this invention that only a single type be utilized.

The precipitation nuclei must be deposited on the surface of the substrate, and it is preferred that they be deposited on the surface by deposition of the composition in a vacuum. For most types of precipitation nuclei it is desirable that the pressure be no greater than about l0 mm. Hg, and in many instances it is preferred that the pressure be 10* mm. Hg, or lower. Accordingly, it is especially preferred that the vacuum deposition take place under a pressure of from about 0.1 to about 1X10 mm. Hg.

The precipitation nuclei are generally deposited on the surface by melting the material in a suitable receptacle under vacuum and exposing the substrate surface to the molten material. In a preferred embodiment, the surface of the substrate is passed continuously over the receptacle so as to produce a coating of the composition on the surface. It will be understood that a heavy coating of the composition is not necessary, and may in fact be undesirable. Accordingly, it is preferred that no more than a monomolecular or monatomic layer be used.

The vacuum deposition can be carried out on batches of the substrate or continuously. In a preferred embodi ment of the invention the substrate is passed across an aperture over melted precipitation nuclei material in a vacuum to deposit the desired amount of the material on the substrate. Generally, the substrate is exposed to molten precipitation nuclei composition for periods of time ranging from about 0.1 to about seconds.

It will be understood that where the silver halide emulsion forms a negative image on development, a positive image will be formed on the substrate of this invention, and when the silver halide emulsion forms a positive image, as for example where it is used to make a print, the substrate of this invention will have a negative image. Thus, it would be possible to have either a print for immediate viewing after the silver halide negative has been developed or a negative for immediate use after a posi tive print has been developed according to this invention. The image formed on the substrate of this invention will be called a reverse visible image to denote that the image produced thereon has reflectance or transmittance properties inverse to that of the developed silver halide emulsion.

The process of developing the silver halide emulsion and forming the reverse visible image on the substrate is conveniently carried out by saturating the substrate with an appropriate monobath developer. A monobath developer contains both the reducing agents known as developers and silver halide-solvent or -solubilizing agents, also called fixers. The monobath developer can additionally contain other conventional auxiliary agents such as antioxidants, accelerators, antifoggants, hardeners, and the like. Basically however, the monobath developer is the combination of an organic reducing agent and a silver halide solvent.

It is well understood by those skilled in the art that the monobath developer is formulated for the particular temperature and other conditions of use so that the developer component has sufiicient opportunity to reduce the exposed silver halide before the halide solvent removes the unexposed halide. Conventional developers such as metol, l-phenyl-3-pyrazolidone, hydroquinone, glycin, pphenylene-diamine, p-aminophenol, pyrogallol, catechol, ascorbic acid, and the like can be utilized. The halide solvent, or fixer, is conveniently a thiosulfate and can also be a solvent such as a thiocyanate, cyanide, or the like. It is preferred to use the alkali metal or ammonium salts of the foregoing acid radicals.

The saturated substrate is brought into intimate surface contact with the emulsion layer of an exposed silver halide emulsion, and the liquid monobath contained in the substrate diffuses into the emulsion layers to cause simultaneous development of the exposed silver halide and removal of the unexposed silver halide. As the silver halide-complexing agent in the monobath dissolves the halides in the unexposed areas of the emulsion, the silver complex diffuses into the surface of the substrate. The silver complex, upon contact with the precipitation nuclei, decomposes in the presence of the alkaline developer, and metallic silver deposits on the nuclei to form the reverse visible image. After all the exposed silver halide has been re duced to metallic silver, the surfaces are separated and a direct visible image is obtained on the emulsion, while a reverse visible image is obtained on the substrate of this invention.

The following examples are given to illustrate preferred embodiments of this invention as it is now preferred to practice it. It will be understood that these examples are illustrative, and the invention is not to be considered as restricted thereto except as indicated in the appended claims.

EXAMPLE I A Veeco 400 evaporation chamber is used to deposit the precipitation nuclei on the substrate. This evaporation chamber comprises a bell jar capable of being lowered over an electrically heated vessel which carries the precipitation nuclei composition, associated electrical circuitry for heating the vessel to vaporize the composition, and equipment for producing, maintaining, and measuring the vacuum in the bell jar.

A microporous polyvinyl chloride web is affixed to a cardboard mount and maintained at a height of 15 inches above a tungsten foil vessel. Beads of 99.999% pure silver are loaded into the vessel, and the bell jar is lowered over the assembly onto the base plate. The system is evacuated to a pressure of 10- mm. Hg and the vessel temperature is raised by electrical resistance heating to the 960 C. melting point of silver, as determined visually. The microporous polyvinyl chloride is exposed to the molten silver in the vacuum for one minute. The current to the silver-containing tungsten boat is then turned off, the silver is allowed to cool, and pressure in the bell jar is returned to ambient atmospheric pressure.

The nuclei-bearing polyvinyl chloride is then slit into 16 mm. widths and spliced between tWo 16 mm. strips of untreated polyvinyl chloride to provide a control. The following monobath developer is prepared:

Ingredient: Concentration (g./l.) Sodium sulfite 45 Hydroquinone 40 1-phenyl-3-pyrazolidone 2 Sodium hydroxide 32 S-methylbenzOtriazole 0.2 Potassium aluminum sulfate 5 Sodium thiosulfate 160 Water to make one liter.

This monobath developer is adjusted to pH 12.5.

EXAMPLE II The procedure of Example I is repeated with a deposition time of 5 minutes. A good positive image is obtained on the vacuum-coated polyvinyl chloride substrate.

EXAMPLE III The procedure of Example II is repeated utilizing an effective aperture of f/5.6, and a good positive image is obtained on the precipitation nuclei-coated substrate.

EXAMPLE IV The procedure of Example I is repeated utilizing a conical tungsten basket in lieu of the tungsten foil vessel.

A positive image is obtained on the silver precipitation nuclei-coated polyvinyl chloride substrate.

EXAMPLE V A continuous transport system is utilized in the Veeco 400 evaporation chamber so that the substrate can be continuously coated. The transport system is driven through a flexible cable by a A1-H.P., 1725 rpm. motor equipped with a variable speed drive. Thus, the transport system can be used to drive the substrate at a constant rate of speed, and vacuum conditions can be maintained in the bell jar during a run. The amount of precipitation nuclei material to be deposited is controlled by the use of a variable aperture across which the web passes. It is found that such a transport system produces a more uniform deposition of nuclei on the substrate. The tungsten boat used to evaporate the precipitation nuclei composition is equipped with a chromelalumel thermocouple by spot-welding the thermocouple to the boat so temperature readings can be obtained during the course of a run.

Metallic silver is placed in the boat, a 10 mm. Hg vacuum is drawn in the bell jar, the silver is heated to 980 C., and the microporous polyvinyl chloride substrate is passed across the aperture at a speed such that it is exposed to the silver vapor for ten seconds. After coating, the substrate is withdrawn from the bell jar, and used to process a Kodak Special High-Definition Aerial film, Type SO243 silver halide emulsion which has been contact exposed to a resolution target in an Edgerton, Germeshausen, and Grier Model VI sensitometer for ,6 of a second With target exposures varying from a neutral density filtration of 2.3 to 3.8 in one-stop increments (log E=0.3). The monobath-saturated substrate is contacted With the exposed silver halide emulsion for five minutes at 70 F. to develop the emulsion. A positive image having a resolution of 22.7 lines/mm. is obtained on the substrate.

EXAMPLE VI The procedure of Example V is repeated utilizing a nuclei deposition time of 15 seconds. The positive image obtained on the substrate has a resolution of 25.6 lines/ EXAMPLE VII The procedure of Example V is repeated utilizing a deposition time of 50 seconds. A positive image having a resolution of 25 .6 lines/ mm. is obtained on the substrate.

EXAMPLE VIII The procedure of Example V is repeated utilizing a deposition time of 130 seconds. A positive image having a resolution of 16.0 lines/ mm. is obtained on the substrate.

EXAMPLE IX The procedure of Example V is repeated with a deposition time of 7.5 seconds and a silver temperature of 1080 C. A positive image having a resolution of 16.0 lines/mm. is obtained on the substrate.

EXAMPLE X The procedure of Example V is repeated using gold as the nucleating center composition deposited from a tungsten boat at a temperature of 1075 C. under conditions such that the deposition time is 5.4 seconds. A positive image having a resolution of 28.5 lines/mm. is obtained, using exposure conditions of second at 1.8 to 3.5 neutral density filtration on the sensitometer.

EXAMPLE XI The procedure of Example X is repeated with a deposition time of 13 seconds. A positive image having a resolution of 22.7 lines/mm. is obtained on the polyvinyl chloride substrate.

7 EXAMPLE XII The procedure of Example X is repeated using a deposition time of 30 seconds and a temperature of 1170 C. A positive image having a resolution of 28.5 lines/mm. is obtained on the polyvinyl chloride substrate.

The foregoing examples illustrate the use of a porous Web for processing. It will be understood that the web can either be saturated with the monobath developer or the monobath developer can pass through the web from a reservoir in which it and the halide emulsion are immersed.

In another aspect of this invention, a hydrophilic layer such as gelatin is carried on a support, as disclosed above. This hydrophilic layer should retain and be capable of releasing sufiicient developer in a reasonable length of time to process the exposed halide emulsion. Accordingly, it is preferred that the hydrophilic layer be capable of releasing a minimum of 2 g./ft. of the monobath developer. Moreover, the hydrophilic layer should maintain its integrity and separate easily from the process halide emulsion. The hydrophilic layer must also resist excess dehydration since the precipitation nuclei are deposited on its surface in a vacuum.

EXAMPLE XIII EXAMPLE XIV The procedure of Example XIII is repeated using gold precipitation nuclei material at a temperature of 1080 C. to prepare the substrate. The Type SO-243 film is exposed in the Model VI sensitometer at second with neutral density filtration of 0.8 to 2.3 and developed in contact with the nuclei-coated cleared film for 5 minutes at 70 F. A negative image is obtained on the aerial film and a positive image is obtained on the nuclei-coated substrate.

EXAMPLE XV The procedure of Example XIV is repeated with silver sulfide as the precipitation nuclei material. A negative image is obtained on the halide emulsion and a positive image is obtained on the nuclei-coated substrate.

EXAMPLE XVI The procedure of Example XIII is used to produce a hydrophilic layer surface containing silver precipitation nuclei. When the material is used to process Type 50-243 aerial film for 5 minutes at 70 F. a positive image having a resolution of 64 lines/mm. is obtained. A commercial diffusion transfer processing material in which the precipitation nuclei are distributed throughout the hydrophilic layer is found to have a resolving power of only 40 lines/mm. under the same contact exposure and processing conditions.

EXAMPLE XVII The equipment described in Example V is used to deposit silver precipitation nuclei on cleared film. The silver is de osited f om a p ss d t ng n b a f r 30 seconds. After deposition the coated substrate is used to process a silver halide emulsion exposed in the Model VI sensitometer for second with neutral density filtration in increments from 2.3 to 3.8. A good positive image is obtained on the substrate during development of the halide emulsion for five minutes at 70 F.

EXAMPLE XVIII The procedure of Example XVII is repeated at a nuclei deposition time of 60 seconds. A good positive image is obtained on the substrate during development of the halide emulsion.

What is claimed is:

1. A process for developing an exposed silver halide emulsion which comprises contacting the emulsion in the presence of a monobath developer with the surface of a microporous polyvinyl chloride substrate permeable to monobath developer for a time sutficient to develop the emulsion and to produce a reverse visible image on the substrate, said substrate having vacuum deposited substantially only on the surface thereof not substantially more than a monomolecular layer of precipitation nuclei.

2. The process of claim 1 wherein the nuclei are selected from the group consisting of metals of Group I-B, II-B, IV-A, and VIII; the sulfides, selenides, and tellurides of said metals; and metals from Group VI-A.

3. The process of claim 1 wherein the nuclei are selected from the group consisting of silver, gold, mercury, tin, and lead and the sulfides of such metals.

4. The process of claim 1 wherein the nuclei are selected selected from the group consisting of silver and gold.

5. The substrate having a reverse visible image thereon produced according to the process of claim 1.

6. A microporous polyvinyl chloride substrate permeable to monobath developer and having deposited substantially only on a surface thereof not substantially more than a monomolecular layer of precipitation nuclei adapted to form a reverse visible image by contact with an exposed silver halide emulsion while said surface and the emulsion are in contact with each other, said substrate being saturated with monobath developer.

7. A microporous polyvinyl chloride substrate according to claim 6 wherein the precipitation nuclei are selected from the group consisting of metals of Groups I-B, II-B, IV-A, and VIII; the sulfide, selenides, and tellurides of said metals; and metals of Group VIA.

8. A microporous polyvinyl chloride substrate according to claim 6 wherein the precipitation nuclei are selected from the group consisting of silver, gold, mercury, tin, lead, and the sulfides thereof.

9. A microporous polyvinyl chloride substrate according to claim 6 wherein the precipitation nuclei are gold NORMAN G. TORCHIN, Primary Examiner I E. CALLAGHAN, Assistant Examiner U.S. Cl. XR 

